Question
Zygote with zona pellucida reaches uterine cavity by :
| A. |
2 days |
| B. |
4 days |
| C. |
5 days |
| D. |
6 days |
Show Answer
|
Correct Answer » B Explanation |
 |
After fertilization in the ampulla of the fallopian tube, the zygote undergoes successive mitotic divisions (cleavage) while traveling towards the uterus.
- Day 1: Two-cell stage
- Day 2: Four-cell stage
- Day 3: Morula (12–16 cells)
- Day 4: Early blastocyst reaches the uterine cavity, still enclosed within the zona pellucida.
- Day 5: The zona pellucida degenerates (hatching), allowing the blastocyst to implant.
- Day 6–7: Implantation begins in the endometrium.
Thus, the zygote/blastocyst with the zona pellucida reaches the uterine cavity on approximately the 4th day after fertilization.